The alkylation of benzene with ethylene over a molecular sieve catalyst is a well-known procedure for the production of ethylbenzene. Typically, the alkylation reaction is carried out in a multistage reactor involving a feedstream of benzene and ethylene to the front of the reactor with the interstage injection of ethylene and benzene to produce an output from the reactor that involves a mixture of monoalkyl and polyalkylbenzene. The principal monoalkylbenzene is, of course, the desired ethylbenzene product. Polyalkylbenzenes include diethyl benzene, triethylbenzene, and xylenes.
With the passage of time, the catalyst becomes deactivated. The alkylation reaction is an exothermic reaction which is accompanied by the deposition of coke on the catalyst bed. The degree of deactivation can be determined by sensing the exotherm as it moves progressively through the catalyst bed from the inlet side to the outlet side of the reactor.
In many cases, it is desirable to operate the alkylation reactor in conjunction with the operation of a transalkylation reactor in order to produce additional ethylbenzene through the transalkylation reaction of polyethylbenzene with benzene. The alkylation reactor can be connected to the transalkylation reactor in a flow scheme involving one or more intermediate separation stages for the recovery of ethylene, ethylbenzene, and polyethylbenzene.
Transalkylation may also occur in the initial alkylation reactor. In this respect, the injection of ethylene and benzene between stages in the alkylation reactor not only results in additional ethylbenzene production but also promotes transalkylation within the alkylation reactor in which benzene and diethylbenzene react through a disproportionation reaction to produce ethylbenzene.
Various phase conditions may be employed in the alkylation and transalkylation reactors. Typically, the transalkylation reactor will be operated under liquid phase conditions, i.e., conditions in which the benzene and polyethylbenzene are in the liquid phase, and the alkylation reactor is operated under gas phase conditions, i.e., pressure and temperature conditions in which the benzene is in the gas phase. However, liquid phase conditions can be used where it is desired to minimize the yield of undesirable by-products from the alkylation reactor.